1. Field of the Invention
The present invention relates to a control device capable of optimally adjusting in accordance with work content the responsiveness of a hydraulic system in hydraulically-operated equipment, comprising a hydraulic shovel, crane and other construction machinery.
2. Description of the Related Art
Hydraulically-operated equipment such as construction equipment is generally provided with a hydraulic pump 2, which is driven in accordance with a motor (engine) 1, and constitutes a hydraulic system, as shown in FIG. 1, so that the pressure oil discharged from this hydraulic pump 2 is supplied to various hydraulic actuators 3, 4. In this case, the orifice size of various flow control valves 5, 6 is changed respectively in accordance with the operation quantity of a plurality of operation levers 7, 8, and the discharge pressure oil of the hydraulic pump 2 is distributed to the respective hydraulic actuators 3, 4.
There are various kinds of systems for controlling the swash plate of a hydraulic pump 2, but in general, when an operation lever 7, 8 is operated, the position of the swash plate 2a of the hydraulic pump 2 (pump displacement q (cc/rev)) is controlled so that the discharge quantity of the hydraulic pump 2 increases in accordance with the magnitude of the operation quantity thereof. In accordance therewith, the flow required by the operation of the operation lever 7, 8 is supplied to the respective hydraulic actuator 3, 4. The position of the swash plate 2a of the hydraulic pump 2 (pump displacement q (cc/rev)) is changed in accordance with a drive signal, that is, a flow command r outputted from a controller 30 to a mechanism 31, which drives the swash plate 2a of the hydraulic pump 2.
Herein lies a need to enhance workability by optimally controlling in accordance with work content the responsiveness of signals outputted relative to the inputted signals of a hydraulic pump 2 and other hydraulic control apparatus in a hydraulic system such as this.
For example, when work is to be carried out rapidly, the desire is to heighten responsiveness so that hydraulic actuators 3, 4 and the work machine driven thereby are driven with good responsiveness in accordance with the operation of the operation levers 7, 8. Further, for work that requires fine control, it is desirable to lower responsiveness so that even if operation levers 7, 8 are operated fully in haste, the work machine is not quick to follow suit.
In particular, there are cases wherein it is desirable to lower responsiveness in accordance with work content even in a hydraulic system, which is constructed so that the response of each individual hydraulic control apparatus is sufficiently large.
Accordingly, technology related to heightening this kind of workability is disclosed in Japanese Patent Laid-open No. 9-151859.
In the invention disclosed therein, when the load pressure of a hydraulic cylinder, hydraulic motor, or other hydraulic actuator suddenly increases, to prevent hydraulic pump discharge pressure from rising, and the number of revolutions of the motor (engine) driving the hydraulic pump from dropping, the change in hydraulic pump discharge pressure is detected, and when this discharge pressure change exceeds a predetermined value, the discharge quantity of the hydraulic pump is reduced, and the load acting on the motor is decreased. In accordance therewith, a drop in the number of revolutions of the motor is prevented in advance.
However, if the hydraulic pump load suddenly changes in accordance with this control, even though a drop in engine revolutions is prevented by reducing the pump discharge quantity in accordance with the magnitude of the hydraulic pump pressure change, in a situation, wherein engine revolutions do not drop, and for light load work, in which the change in hydraulic pump discharge pressure or discharge flow is small, with regard to the behavior of the hydraulic pump, it is the same as if no control is performed, and there is no change in the responsiveness of the hydraulic pump.
In general, for a hydraulic system, which sufficiently enhances the responsiveness of the hydraulic pump unit to improve the workability of "skeleton work" and "bucket sifting work", which require work machine responsiveness, when attempting to perform work, which requires extremely fine control, such as "correction and finishing work", there is the reverse problem that the hydraulic pump responds sensitively to hydraulic pump load pressure and operation lever operation, causing fine control capabilities to be lost. Consequently, skill is required to operate the operation levers when performing fine control work, placing a big burden on the operator.
Further, with the technologies disclosed Japanese Patent Publication No. 4-51670 and Japanese Patent Application Laid-open No. 6-200878, to prevent hydraulic pump discharge pressure from suddenly fluctuating or hunting when a work machine is suddenly put into operation, either a differential value of the hydraulic pump discharge pressure is calculated, or a pressure fluctuation component of a peculiar vibration frequency component determined beforehand in accordance with the hydraulic pump is calculated from a hydraulic pump discharge pressure signal, and this calculated value is subtracted from the hydraulic pump discharge flow command value. In accordance therewith, the fluctuation of the hydraulic pump discharge pressure is prevented from continuing, and the vibration characteristics of the hydraulic pump are enhanced.
However, even though it is possible to move toward curbing hydraulic pump discharge pressure vibration in accordance with this control, when performing work in which it is not desirable to suppress vibration, it is not possible to lower the responsiveness of the hydraulic pump in a direction that does not curb vibration. In other words, hydraulic pump responsiveness could not be changed in accordance with the work content.
Thus, load sensing control, negative pump control, and positive pump control are the usual control systems for a hydraulic pump.
First, load sensing control will be explained.
With the invention disclosed in Japanese Patent Application Laid-open No. 7-197907, in so-called load sensing control (hereinafter referred to as LS control for convenience sake), the differential pressure between hydraulic pump discharge pressure and maximum load pressure is detected, and control is performed by multiplying control gain relative to the flow command for the hydraulic pump so that this differential pressure constitutes the target differential pressure value. In this case, the operation quantity of the operation lever is detected, and control gain is increased in accordance with the increases in operation quantity, so that the deviation between target differential pressure and actual differential pressure is reduced more rapidly when operation quantity is large, thus enhancing the quick reaction capabilities of the hydraulic pump. And when the operation quantity of the operation lever is small, the deviation between the above-mentioned differential pressures is reduced relatively slowly by decreasing control gain so that the discharge flow of the hydraulic pump is made to change smoothly. Furthermore, load sensing control is one system for controlling the swash plate of a hydraulic pump, and controls the hydraulic pump swash plate so that the hydraulic pump discharge pressure is always higher by the magnitude of a predetermined target differential pressure than the maximum value of the load pressure (hereinafter referred to as the maximum load pressure) of the hydraulic actuator during operation.
Next, negative pump control will be described.
Negative pump control (hereinafter referred to as negative control for convenience sake) is a pump control system, which controls the swash plate of a pump so that the flow discharged from the center by-pass circuit to a tank is constant, and is designed to change the time it takes for the hydraulic pump discharge flow to reach a target flow by multiplying control gain of a magnitude that corresponds to the operation quantity of an operation lever by the flow command relative to the hydraulic pump. Furthermore, negative pump control is a system for controlling the swash plate of a hydraulic pump, and provides a center by-pass circuit, which discharges pressure oil inputted from the hydraulic pump to a tank via a flow control valve. The flow control valve increases the closing of the above-mentioned center by-pass circuit from a neutral state in accordance with the performance of a stroke, and also detects the flow discharged to the tank. As this flow becomes smaller, the negative control system controls the hydraulic pump swash plate so that the flow discharged from the hydraulic pump increases, making the flow discharged from the center by-pass circuit to the tank constant.
However, with the invention disclosed in this Japanese Patent Application Laid-open No. 7-197907, since control gain is simply multiplied by the flow command signal to the hydraulic pump, control deviation increases when control gain becomes small. That is, when carrying out a level fine control operation, in which the operation quantity of the operation lever is small, it is a problem in that normal state controllability worsens as a result of increased control deviation.
Further, as a pump control system other than the above-mentioned LS control and negative control, there is what is called positive pump control (hereinafter referred to as positive control for convenience sake), which detects the operation quantity of an operation lever, and controls the hydraulic pump swash plate so that a discharge volume (supply flow) corresponding to the sum of the operation quantity thereof (operator required flow) is discharged from the hydraulic pump.
However, in this positive control system, there is no control deviation, and the above-described control, wherein control gain is multiplied by a flow command, cannot be employed.
Conversely, in the above-mentioned positive control system, it might be possible to provide a sensor, which detects the position of the hydraulic pump swash plate, and to find the deviation between this detected position and a target position, and multiply same by control gain. However, to provide anew such a sensor to an existing positive control system would raise system construction costs. But without adding new hardware to an existing positive control system, control, wherein control gain is multiplied by a flow command, will not be possible.
Further, the invention disclosed in Japanese Patent No. 2651079 is constituted so that the change speed of the hydraulic pump swash plate inclined rotation angle (discharge volume) is selected in accordance with a switch operation by an operator, and hydraulic pump discharge volume is controlled by control gain corresponding to the selected speed.
However, in the art disclosed therein, the problem is that the response speed of the hydraulic pump must be switched using a switch operation each time work content differs, making operation troublesome. Furthermore, the nature of the control of the invention disclosed in this Patent No. 2651079 is the same as that disclosed in the above-mentioned Japanese Patent Application Laid-open No. 7-197907, giving rise to the problem that controllability deteriorates when performing work that requires fine lever control.
Further, the invention disclosed in Japanese Patent No. 2628418 is constituted so that flow control valve responsiveness can be changed by selecting the time until the flow of pressure oil supplied from the flow control valve to a hydraulic actuator reaches a command value.
However, the problem is that the art disclosed therein, similar to that disclosed in the above-mentioned Japanese Patent No. 2651079, requires that flow control valve responsiveness be switched using a switching operation, making for troublesome operation.
Furthermore, the nature of the control of this Japanese Patent No. 2628418 is such that, as shown in FIG. 23(b), control is performed by merely decreasing response time by decreasing the time change of an input signal (FIG. 23(a)), and does not perform control, wherein, as shown in FIG. 23(c), detects a quantity of state different from the input signal, and holds responsiveness in check by compensating the input signal in a direction, which hinders a change in this quantity of state. When performing the control of this Japanese Patent No. 2628418, an output signal is simply delayed relative to an input signal, making it impossible to achieve sufficient steadiness and quick reaction capabilities.